regarding PSS and PAC analysis

Hello.

I'm trying to simulate an N path filter circuit.

I used to deal with analog circuits and not RF ciruits, so im always used to run an AC analysis that follows a DC operating point analysis.

to my understanding, regarding LPTV systems PSS is equivalent to finding the DC operating point, and PAC is equivalent to finding the AC response (for different harmonies).

That being said, I am confused regarding what should be the input when I set the PSS analysis.

Say my LO is at 1 GHZ, what should be the proper Vin I need to set? at what frequency, if any? if I assume the input is always gonna be small signal, should I even provide other DC than zero?

I tried setting Vin to zero DC, then to 1Ghz sinus at different amplitudes, and even at other frequencies. each time, i'm getting different PAC frequency responses.

See the attached circuit schematic (I assume this is a common topology). 

Thanks in advance.